Loading ...
Sorry, an error occurred while loading the content.

GEOSTATS: Random vectors

Expand Messages
  • Colin Daly
    Hi, I hope this doesn t constitute what Gregoire calls a very stupid problem! 1) Does anyone know a free/cheap plotting tool for vector fields. (At each point
    Message 1 of 2 , Feb 1, 1999
    • 0 Attachment
      Hi,

      I hope this doesn't constitute what Gregoire calls a very stupid
      problem!

      1) Does anyone know a free/cheap plotting tool for vector fields. (At
      each point x of a 3d (or 2d) array, I have a vector v(x). Thus my plot
      will be lots of little arrow)

      2) Has anyone done any work or heard of any work on Random Tensor
      fields. I've made a start and got somewhere (for what it's worth) but I
      don't want to reinvent the wheel.

      Colin



      --
      *To post a message to the list, send it to ai-geostats@....
      *As a general service to list users, please remember to post a summary
      of any useful responses to your questions.
      *To unsubscribe, send email to majordomo@... with no subject and
      "unsubscribe ai-geostats" in the message body.
      DO NOT SEND Subscribe/Unsubscribe requests to the list!
    • Colin Daly
      My original message to the site was as follows ... It s been so long since I sent this that I guess some of you will have retired and your children will be
      Message 2 of 2 , Feb 15, 1999
      • 0 Attachment
        My original message to the site was as follows

        > Hi,
        >
        > I hope this doesn't constitute what Gregoire calls a very stupid
        > problem!
        >
        > 1) Does anyone know a free/cheap plotting tool for vector fields. (At
        > each point x of a 3d (or 2d) array, I have a vector v(x). Thus my plot
        > will be lots of little arrow)
        >
        > 2) Has anyone done any work or heard of any work on Random Tensor
        > fields. I've made a start and got somewhere (for what it's worth) but I
        > don't want to reinvent the wheel.
        >
        > Colin
        >

        It's been so long since I sent this that I guess some of you will have
        retired and your children will be reading my final response. So for those
        who replied - sorry it took me so long to get back!

        Anyhow - I had a good number of replies and some people wanted to get
        replies forwarded so here they are

        1) Pat Lapcevic has a homemade (fortran) program which I'm going to try
        and get hold of. He also suggests GRIDBUILDER - a finite element grid
        builder from Rob McLaren (email mclaren@...). He doesn't
        know the cost and I've not yet got a reply from Rob.

        2) Med Bennett suggests some IDL commercial software (@:$1500). Check it at
        http://www.rsinc.com

        Another commercial suggestion was from C TECH Development
        http://www.ctech.com

        3) Denis Marcotte informs us that Matlab has Quiver and Quiver3 for 2 and 3d
        respectively.

        ... while GillesG@... suggests a SCI-LAB solution. Sci-Lab being a
        Matlab type solution. Information at
        http://www-rocq.inria.fr/scilab/scilab.html
        Download from ftp://ftp.inria.fr/INRIA/Projects/Meta2/Scilab

        4) Denis Allard and Katherine Campbell tell us that (at least) in 2d there
        is an Splus solution to plotting vectors and Katherine provides us with some
        code

        plot(lrange$x,lrange$y,type="n",axes=F,xlab="",ylab="")
        draw.vectors(slope[1:2,,])


        draw.vectors <- function(z) {
        # Assume z is 2 x n x m
        n <- dim(z)[2]
        m <- dim(z)[3]
        zmax <- max(sqrt(z[1,,]^2+z[2,,]^2))
        tz <- 0.5*z/zmax
        for (i in 1:n) {
        for (j in 1:m) {
        arrows(i-tz[1,i,j],j-tz[1,i,j],
        i+tz[1,i,j],j+tz[2,i,j],
        size=.02,open=T,rel=F)
        }
        }
        }

        Thanks for that Katherine

        5) alistair@... has seen some stuff in SAS which he believes to be
        usefull.

        6) Dan Cornford suggests the NEUROSAT page for some work on wind field
        models for random vector fields and asks when or where we might meet random
        tensor fields.

        Well a quick reply is to note that Permeability, Stress, Strain etc. etc.
        are 2nd order tensors - their covariances need to expressed fully with a 4th
        order tensor. They tend to occur quite often when modelling Petroleum
        reservoirs - although in practice there is usually no need to consider the
        general case and the tensor is treated as diagonal.

        As we know, the class of isotropic covariance functions in 3d is a subclass
        of the 1d covariance functions (eg the 1d spherical (or triangular model) is
        not +ve definite in 3d). From here, you can ask yourself what are the
        conditions for isotropy of a random vector field (eg. Yaglom 1986) - that
        is when the covariance is independent of the choice of orthogonal co-ord
        system. It turns out that this imposes some restrictions on the form of
        covariance function (Yaglom). I was just looking at how this generalises to
        tensors. (The real purpose for me was to check the functional form of a
        covariance tensor that was provided by a third party - as it's behavior
        seemed a bit odd)

        Anyhow - many thanks to all who replied. I'll check things out in a bit
        more detail and if anything blows me away I'll be sure to pass it on.

        Colin




        --
        *To post a message to the list, send it to ai-geostats@....
        *As a general service to list users, please remember to post a summary
        of any useful responses to your questions.
        *To unsubscribe, send email to majordomo@... with no subject and
        "unsubscribe ai-geostats" in the message body.
        DO NOT SEND Subscribe/Unsubscribe requests to the list!
      Your message has been successfully submitted and would be delivered to recipients shortly.